Sinter-hardening powder and their sintered compacts

ABSTRACT

The present invention relates to a sinter hardening powder that can yield a sintered compact with high strength. The present invention provides a raw powder for sintering, comprising Fe as its primary component and also comprising 0.1-0.8 wt % C, 3.5-12.0 wt % Ni, 0.1-7.0 wt % Cr, and 2.0 wt % or less of Mo, wherein the mean particle size of the raw powder for sintering is 150 μm or less. The sintered compact having high tensile strength, high hardness, and good ductility can be formed without performing the quenching process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of a prior application Ser.No. 10/907,155, filed on Mar. 23, 2005, now pending, which claims thepriority benefit of Taiwan application serial no. 93116634, filed onJun. 10, 2004 and Taiwan application serial no. 93126297, filed on Sep.1, 2004. All disclosures are incorporated herewith by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to raw powders, in particular,to compositions of sinter hardening powders useful for forming highhardness and high strength parts by the powder metallurgy (P/M) process.

2. Description of Related Art

As is well known in the art, the design of the alloy is always thecritical starting point for the development of powder metallurgy. Bycombining different alloying elements and different amounts ofadditives, various alloy steels can be developed and applicable todiversified circumstances. In general, powder metallurgy components arerequired to possess high density, good dimensional control, and goodmechanical properties. Thus, different alloys are developed. One exampleto enhance the sintered density and dimensional control of sinteredcompacts is described in US2005/0109157, in which a prealloyed steelpowder is used, in contrast to the elemental powder or mixtures ofelemental powder and ferroalloy powder of the present invention. Anotherexample to enhance the hardness, strength, or ductility of sinteredcompacts is by adjusting the alloying elements, as is disclosed in U.S.Pat. No. 5,476,632. To attain better mechanical properties, mostsintered components require a hardening heat treatment like quenchingfollowed by tempering.

However, while the quenching is performed on the sintered components,several problems such as deformation, size inconsistency, or crackingmay be caused by the fast cooling procedure. In addition, the heattreatment (quenching) performed on the sintered components will causeadditional costs. Therefore, sinter-hardening powders have beendeveloped by adding high hardenability alloying elements such asmolybdenum (Mo), nickel (Ni), manganese (Mn) or chromium (Cr) to ironpowders. The sinter-hardening powders are pressed out to form a greencompact through the conventional compacting process. Thereafter, thegreen compact is sintered so as to obtain a sintered compact with thehardness above HRC30. Examples of alloys (i.e. sintered compacts)produced by the above-mentioned method are Ancorsteel 737SH(Fe-0.42MN-1.40Ni-1.25Mo—C) from Hoegananes Corp. and ATOMET 4701(Fe-0.45Mn-0.90Ni-1.00Mo-0.45Cr—C) from Quebec Metal Powders Limited.The sintered components made from these sinter-hardening powders arecooled at rates of a minimum of 30° C. per minute in the sinteringfurnace in order to generate martensite and bainite.

Although the alloying elements in these sintered compact are still nothomogenized completely using the regular sintering conditions of 1120°C. and 30-40 minutes, these sinter-hardening powders provide bettermechanical properties than those possible using non sinter-hardeningpowders. Although the sinter-hardening powders can reduce costs due tothe elimination of the quenching process, a high cooling rate system hasto be installed in the sintering furnace. Furthermore, theaforementioned cooling rates, while slower than those of quenching intooil or water, are still fast enough to cause problems such asdeformation, inconsistency of the dimensions, and even cracking.According to U.S. Pat. No. 5,682,588, the claimed powders are compactedby the conventional pressing process, specifically, the claimed powdersare sintered between 1130-1230° C., and then cooled at rates of 5-20°C./minute in order to reach the desired sinter-hardening effects. Thishas improved the process by lowering the minimum cooling rate of30′/min, as described in the previously mentioned processes. However,the mechanical properties, in particular, the ductility, are stillunsatisfactory.

Concerning the press-and-sinter process, there are several materialstandards (the latest Year 2003 version) for sinter hardened alloys setforth by the Metal Powder Industries Federation (MPIF), for example,FLNC-4408 (1.0-3.0% Ni, 0.65-0.95% Mo, 1.0-3.0% Cu, 0.6-0.9% C, and theremaining portion is Fe) and FLC2-4808 (1.2-1.6% Ni, 1.1-1.4% Mo,1.0-3.0% Cu, 0.3-0.5% Mn, 0.6-0.9% C, and the remaining portion is Fe).After sintering and tempering, the above-mentioned sinter hardeningalloy of FLC2-4808 can reach a tensile strength of 1070 MPa under thedensity of 7.2 g/cm³, and the hardness can reach HRC40, while theelongation is less than 1.0%. Although this alloy is a sinter-hardeningtype, its mechanical properties are still not satisfactory, particularlythe elongation, and the required cooling rate is still very fast.

In the field of metal injection molding process, the powders used areusually less than 30 μm in size, while the particles used in thepress-and-sinter process are less than 150 μm in size. Since thediffusion distances in fine powers are shorter, the added alloyingelements can be homogenized more easily in the matrix materials.Therefore, sintered compacts sintered from the fine powders possessmechanical properties better than those of the traditionalpressed-and-sintered components. At present, the alloys commonly usedfor metal injection molding are the Fe—Ni—Mo—C alloy series, exemplifiedby MIM-4605 (1.5-2.5Ni, 0.2-0.5% Mo, 0.4-0.6% C, <1.0% Si, the remainingportion is Fe), which has the best mechanical properties according tothe MPIF standards. This alloy, after sintering, reaches a tensilestrength of 415 MPa, a hardness of HRB62, and a ductility of 15%. Inorder to attain the best mechanical properties, the sintered product hasto be heat-treated (quenched and tempered). It then reaches a tensilestrength of 1655 MPa, a hardness of HRC48, and a ductility of 2.0%.

Although excellent mechanical properties of the metal injection moldedproducts can be obtained by heat treatment after sintering, the costs ofthe heat treatment accounts for a large part of the whole productioncost. Hence, it is critical to lower the costs of the heat treatment,for example, by using sinter-hardening alloys. However, according to theMetal Powder Industries Federation Standards, no sinter-hardening alloysare listed for the metal injection molding process.

As mentioned above, application of fine powders improves the uniformityof the alloying elements and mechanical properties of the products.However, application of fine powders in the traditional press-and-sinterprocess is difficult because of the poor flowability of the powder,which in turn makes it difficult to fill the powders into the diecavity, and thus automated pressing can not be used. However, thisproblem can be overcome by granulating the fine powders into largespherical particles, such as by the spray drying process, and thegranulated powders can then be applied in the press-and-sinter process.

The present invention was achieved in view of the problems such as thosedescribed above for press-and-sinter and metal injection moldingproducts. An object is thus to provide raw sinter hardening powders orgranulated sinter hardening powders for sintering whereby the sinteredcompacts can attain high hardness and high strength without any heattreatment (quenching) and with a slow cooling rate after sintering.

REFERENCE PAPERS

-   1. U. Engström, J. McLelland, and B. Maroli, “Effect of    Sinter-Hardening on the Properties of High Temperature Sintered PM    Steels”, Advances in Powder Metallurgy & Particulate materials-2002,    Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I.    Sanderow, MPIF, Princeton N.J., 2002, part 13, page 1-13.-   2. K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K. Kanto,    “Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a carbon/carbon    Composite Mesh Belt Furnace”, Advances in Powder Metallurgy &    Particulate materials-2002, Compiled by V. Arnhold, C-L Chu, W. F.    Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part    13, page 14-22.-   3. H. Suzuki, M. Sato, and Y. Seki, “Sinter Hardening    Characteristics of Ni—Mo—Mn—Cr Pre-Alloyed Steel Powder”, Advances    in Powder Metallurgy & Particulate materials-2002, Compiled by V.    Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF,    Princeton N.J., 2002, part 13, page 83-95.-   4. D. Milligan, A. Marcotte, J. Lingenfelter, and B. Johansson,    “Material Properties of Heat Treated Double Pressed/Sintered P/M    Steels in Comparison to Warm Compacted/Sinter Hardened Materials”,    Advances in Powder Metallurgy & Particulate materials-2002, Compiled    by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow,    MPIF, Princeton N.J., 2002, part 4, page 130-136.-   5. B. Lindsley, “Development of a High-Performance Nickel-Free P/M    Steel”, K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K.    Kanto, “Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a    carbon/carbon Composite Mesh Belt Furnace”, Advances in Powder    Metallurgy & Particulate materials-2004, Compiled by W. B. James,    and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page    19-27.-   6. B. Hu, A. Klekovkin, D. Milligan, U. Engström, S. Berg, and B.    Maroli, “Properties of High-Density Cr—Mo Pre-alloyed Materials    High-Temperature Sintered”, Advances in Powder Metallurgy &    Particulate materials-2004, Compiled by W. B. James, and R. A.    Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 28-40.-   7. P. King, B. Schave, and J. Sweet, “Chromium-containing Materials    for High-Performance Components”, Advances in Powder Metallurgy &    Particulate materials-2004, Compiled by W. B. James, and R. A.    Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 70-80.-   8. M. Schmidt, P. Thorne, U. Engström, J. Gabler, T. J. Jesberger,    and S. Feldbauer, “Effect of Sintering Time and Cooling Rate on    Sinter Hardenable Materials”, Advances in Powder Metallurgy &    Particulate materials-2004, Compiled by W. B. James, and R. A.    Chernenkoff, MPIF, Princeton N.J., 2004, part 10, page 160-171.-   9. MPIF Standard 35, Materials standards for Metal Injection Molded    Parts, 2000 edition, MPIF, Princeton N.J., pp. 12-13.-   10. MPIF Standard 35, Materials standards for P/M Structural Parts,    2003 edition, MPIF, Princeton N.J., pp. 46-47.-   11. K. S. Hwang, C. H. Hsieh, and G. J. Shu, “Comparison of the    Mechanical Properties of Fe-1.75Ni-0.5Mo-1.5Cu-0.4C Steels made from    the PIM and the Press-and-Sinter Processes”, Powder Metallurgy,    2002, Vol. 45, No. 2, pp. 160-166.-   12. U.S. Pat. No. 5,876,481, 1999.-   13. U.S. Pat. No. 5,834,640, 1998.-   14. U.S. Pat. No. 5,682,588, 1997.-   15. U.S. Pat. No. 5,476,632, 1995.

SUMMARY OF THE INVENTION

The present invention is directed to a sinter hardening powder havingnovel composition and sintered compact manufactured thereby.

The above-mentioned sinter hardening powder and the sintered compactprepared therefrom including iron (Fe), carbon (C), nickel (Ni), andchrome (Cr), in the ratios as follows: Ni: 3.5 wt %-12.0 wt %, carbon:0.1 wt %-0.8 wt %, chrome: 0.1 wt %-7.0 wt %, 2.0% or less of Mo, andthe remaining portion is Fe. Additionally, the mean particle size of thepowder is less than 150 μm. In one embodiment of the present invention,the above composition may further contain at least one other minorstrengthening elements at the amount of 0.5 wt %-5.0 wt %. Thestrengthening elements can be selected from the group consisting ofCopper (Cu), Titanium (Ti), Aluminum (Al), Manganese (Mn), Silicon (Si),and Phosphorous (P). The element carbon mentioned above may be providedby adding graphite or using carbon-containing carbonyl iron powders. Thesintered compact of the above-mentioned sinter hardening powders has ahigh tensile strength, high hardness, and good ductility without the useof any quenching process. Since no quenching process is required, theproduction cost is lower. A higher production yield is also attained dueto the elimination of defects, such as cracks and distortions, which arecaused by the high thermal stress during quenching.

Moreover, the sintered compact fabricated by the conventionalpress-and-sinter or metal injection molding processes can besinter-hardened under the normal cooling rate (3-30° C./minute) insidethe traditional sintering furnace. The sintered compact can be treatedwith low temperature tempering without quenching, to obtain excellentmechanical properties.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and they are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

FIGS. 1(a) and 1(b) show the line scan of Ni in Cr-free sinteredcompacts using an Electron Probe Microanalyzer (EPMA).

FIG. 2 shows that when the Cr content increases, the hardness of thesintered compact produced by using the metal injection molding processand using fine carbonyl iron powders increases slightly first, reachinga maximum at about 0.7 wt %, and then decreases.

FIG. 3 shows that when the Cr content increases, the hardness of thesintered compact produced by using press-and-sinter process and usingcoarse iron powders increases first, reaching a maximum at about 3 wt %,and then decreases.

FIG. 4 is a cross-sectional view of the sample in example 1, observingthe ductile microstructure with dimple type fractures by the scanningelectronic microscope.

DESCRIPTION OF THE EMBODIMENTS

The foregoing descriptions of specific embodiments of the invention havebeen presented for purposes of illustration and description. They arenot intended to be exhaustive or to limit the invention to the preciseforms disclosed. Obviously, many modifications and variations arepossible in light of the above teaching. The embodiments were chosen anddescribed in order to explain the principles and the application of theinvention, thereby enabling others skilled in the art to utilize theinvention in its various embodiments and modifications according to theparticular purpose intended. The scope of the invention is intended tobe defined by the claims appended hereto and their equivalents.

The sinter hardening powder for sintering of the embodiment of thepresent invention includes Fe as its primary component, 0.1 wt %-0.8 wt% of C, 3.5 wt %-12.0 wt % Ni, 0.1 wt %-7.0 wt % Cr, 2.0 wt % or less ofMo, wherein the mean particle size of the sinter hardening powder forsintering is 150 μm or less.

Nickel (Ni) is an element that could yield high hardenability and couldalso give high toughness and elongation of sintered compacts. Thus, itis preferred to add more Ni in the sinter hardening powder forsintering. In the present invention, the Ni content preferred is between3.5 wt % and 12.0 wt %, since the sinter-hardening characteristics arenot obvious when the Ni content is lower than 3.5 wt %. Additionally,the sinter-hardening characteristics diminish when the Ni content ishigher than 12 wt %. In another aspect, the sinter hardening powderbecomes expensive when the Ni content is higher than 12 wt %. However,Ni has a slow diffusion rate into Fe compared to that of Cr, Mo, Cu, andMn, which are the main alloying elements widely used in the industry.Thus, Ni is difficult to be homogenized in the Fe matrix and as a resultloses its sinter-hardening benefits. Moreover, Ni-rich areas are formed.The Ni-rich areas are low in strength and hardness and become thevulnerable sites during mechanical testing and during field operationsthat are under high stresses.

The sinter hardening powder of the present invention may furthercomprise at least one other minor strengthening elements at the amountof 0.5 wt %-5.0 wt %. The strengthening elements may be selected fromthe group consisting of Copper (Cu), Titanium (Ti), Aluminum (Al),Manganese (Mn), Silicon (Si), Niobium (Nb), or Phosphorous (P).Specifically, the content of the strengthening elements may be listed asfollowing: 2 wt % or less Copper (Cu), 1 wt % or less Titanium (Ti), 1wt % or less Aluminum (Al), 1 wt % or less Manganese (Mn), 1 wt % orless Silicon (Si), 1 wt % or less Niobium (Nb), and 1 wt % or less ofPhosphorous (P). In an preferred embodiment of the present invention,the content of Copper (Cu) is between 0.1 wt %-1.0 wt %, the content ofManganese (Mn) is between 0.1 wt %-0.8 wt %, and the content of Silicon(Si) is between 0.1 wt %-0.5 wt %.

In one preferred embodiment of the present invention, the content ofCarbon (C) may be between 0.3 wt %-0.7 wt %, the content of Nickel (Ni)may be between 6.0 wt %-10.0 wt %, the content of chromium (Cr) may bebetween 0.3 wt %-6.0 wt %, and the content of molybdenum (Mo) may bebetween 0.1 wt %-1.0 wt %. The content of the elements of the sinterhardening powder is only for illustration. The scope of the invention isintended to be defined by the claims appended hereto and theirequivalents.

In one embodiment of the present invention, the mean particle size ofthe sinter hardening powders is between 0.1 μm and 30 μm, and thecontent of chromium (Cr) is between 0.1 wt % and 2 wt %. In analternative embodiment of the present invention, the mean particle sizeof the sinter hardening powders is between 30 μm and 150 μm, the contentof chromium (Cr) is between 1 wt % and 6 wt %. In an alternativeembodiment of the present invention, the sinter hardening powders may beelemental powders, ferroalloy powders, or a mixture thereof.

To fully take advantages of the Ni addition, we have found that Craddition significantly improves the homogeneity of Ni. For example, theNi distribution, as shown by the line scan of Ni in FIG. 1(a), is notuniform. When Cr is present, the Ni distribution becomes much improved,as shown by the line scan of Ni in FIG. 1(b). The addition of Cr thusimproves the Ni distribution and eliminates the soft Ni-rich areas.Therefore, the overall hardness of the sintered compacts increases.

FIG. 2 shows that, using a mixture of fine carbonyl iron powders andother alloying powders according to the composition ofFe-8Ni-0.8Mo-xCr-0.5C (x varies from 0 wt %-4 wt %) and using the metalinjection molding process, the hardness of the sinter hardened andtempered specimens increases first, reaching a maximum at about 0.7 wt%, and then decreases as the amount of Cr increases. This means that theamount of 3 wt % Cr is too much for the need to homogenize the Ni.However, when large iron powders are used, the homogenization becomesmore difficult. Thus, the amount of Cr that is required to homogenize Niincreases. This effect is demonstrated by using a mixture of large (meansize of 72 μm) water atomized iron powders and other alloying powdersaccording to the composition of Fe-0.5Mo-4Ni-0.5C and using thepress-and-sinter process. FIG. 3 shows that the hardness increases,reaches the maximum at about 3 wt % Cr, and then decreases as the amountof Cr increases. These examples show that more Cr is required tohomogenize Ni for coarse iron powders than that of using fine ironpowders.

The element ingredients and the mechanical properties of the sinteredcompact are listed in Table 1 and Table 2, repectively, whereas examples1-2 in Table 2 are the sintered compacts made from the metal injectionmolding process; examples 3-6 are the sintered compacts made from thepress-and-sinter process. Table 1 and Table 2 are also used toillustrate the sinter hardening effect of the sinter hardening powderfor the present invention, while examples 1-6 represent the presentinvention and examples A-E are used as the comparison group according tothe available literatures.

EXAMPLE 1

Following the composition as shown in Table 1, the carbonyl iron powdersthat contain C and Si and with a mean particle size of 5 μm are mixedtogether with fine (with a mean particle size less than 15 μm) elementalMo and Ni powders and Fe—Cr and Fe—Mn ferroalloy powders. The admixedpowder was added with 7 wt % of the binder, kneaded in a Z type highshear rate mixer at 150° C. for 1 hour, then cooled to room temperatureto obtain the granulated feedstock. Thereafter, the previously mentionedgranulated feedstock is filled into the injection molding machine toproduce the tensile test bar (e.g. the standard tensile bar from theMPIF-50 standard.). The tensile bar is de-bound under the procedureapplied from the known arts in the industry to remove the binder, thenheating the tensile bar in the vacuum furnace at 1200° C. for two hours,and then cooling to room temperature at a cooling rate of about 6°C./minute between 600° C. and 300° C., so as to reach a hardness ofHRC51 and a ductility of 1.0%. The tensile bar, after being tempered at180° C. for two hours, reaches a tensile strength of 1800 MPa, ahardness of HRC45, and a ductility of 3%, as shown in Table 2. FIG. 4 isa fracture surface of the sample in example 1. The ductilemicrostructure with dimple type fractures is observed using a scanningelectronic microscope. This indicates that products of high hardness,high tensile strength, and high ductility can be produced from thesealloying elements. Take the as-sintered MIM-4605 as an example, which isan injection molding material with the best mechanical properties listedby the MPIF. The properties are 415 MPa, HRB62, and 15% ductility, asshown in example A in Table 2. After quenching and tempering, theimproved MIM-4605 will possess 1655 MPa, HRC48, and a ductility of 2%,as shown in example B in Table 2. MIM-4605 needs to be quenched andtempered to reach the mechanical properties similar to those made by thepresent invention. However, the sintered compact of the presentinvention possesses good mechanical properties without the need forquenching.

EXAMPLE 2

The same processes as disclosed in example 1 but with the compositionslisted in example 2 in Table 1. After tempering, the tensile bar has atensile strength of 1780 MPa, a hardness of HRC45, and a ductility of4%.

EXAMPLE 3

Following the compositions listed in Example 3 in Table 1, theprealloyed Fe-3Cr-1.5Mo powders having a mean particle size of 75 μmwere mixed with fine elemental Ni and graphite powders and 0.8% zincstearate, which served as a lubricant. The mixture was compacted intotensile bars, de-bound at 550° C. for 15 minutes and then sintered at1250° C. for two hours. After tempering, the sinter hardened tensile barwith a density of 7.2 g/cm³ has a tensile strength of 1320 MPa, ahardness of HRC39, and a ductility of 2%.

EXAMPLE 4

The same processes as in example 3, but with the compositions listed inexample 4 in Table 1. The Fe-3Cr-0.5Mo prealloyed powder was mixed withfine elemental Ni, Cu, and graphite powders, and 0.8% zinc stearate.After tempering, the sinter hardened tensile bar has a tensile strengthof 1280 MPa, a hardness of HRC38, and a ductility of 2%.

EXAMPLE 5

The same processes as in example 3, but with the compositions listed inexample 5 in Table 1. The prealloyed Fe-1.5Cr-0.2Mo powders having amean particle size of 72 μm were mixed with fine elemental Ni andgraphite powders and 0.8% zinc stearate. After tempering, the sinterhardened tensile bar has a tensile strength of 1270 MPa, a hardness ofHRC31, and a ductility of 2%.

EXAMPLE 6

Following the compositions listed in example 6 in Table 1, the carbonyliron powders that contains C and Si and with a mean particle size of 5μm are mixed together with fine elemental Mo and Ni powders and Fe—Crferroalloy powder. The powder mixture was mixed together with 1.5 wt %of the binders. The powders, water, and binders (e.g.: Polyvinylalcohol) are blended into a slurry. The slurry is then atomized from thenozzle at high speed and dried by hot air to evaporate the water within.The fine powders are thus bonded with each other by the binder to formgranulated powders with good flowability. The particle size of thegraduated powder is about 40 μm. The previously mentioned granulatedpowders are filled into the die cavity to produce the green tensile barby the automatic compacting machine. The tensile bar is de-bound underthe procedure applied from the known arts in the industry. For example,the temperature will be raised at the rate of 5° C./minute up to 400°C., and then at the rate of 3° C./minute up to 1100° C., maintained forone hour, and then raised at the rate of 10° C./minute up to 1200° C.,and sintering will continue at this temperature for one hour.Afterwards, the tensile bar is cooled as the temperature of the furnacedrops, and the tensile bar is tempered for 2 hours at 180° C. withoutthe use of the quenching process. As shown in the Table 2, the sinterhardened tensile bar has a tensile strength of 1650 MPa, a hardness ofHRC43, and an elongation of 4%.

EXAMPLE A

According to the standards from the MPIF-35, the elements of MIM-4605used in injection molding are shown in Table 1, while the mechanicalproperties of the sintered compact produced by the elements of MIM-4605are shown in Table 2.

EXAMPLE B

The composition of Example B is identical with the composition as inexample A. After the quenching and tempering treatment, products improveenormously in terms of mechanical properties, as shown in Table 2.

EXAMPLE C

According to the MPIF-35 standards, the elements of MIM-2700 used ininjection molding are shown in Table 1, while the mechanical propertiesof the sintered compact produced by the elements of MIM-2700 are shownin Table 2.

EXAMPLE D

According to the MPIF-35 standards, the elements of sinter-hardeningalloy FLC2-4808 (the best sinter-hardened press-and-sinter work piecelisted by the MPIF) are shown in Table 1. The typical mechanicalproperties of sinter hardened FLC2-4808 are 1070 MPa, HRC40, but withless than 1% ductility, as shown in Table 2. The low ductility makes thealloy less suitable for the application of structural parts, whichusually require good ductility.

The comparison of the above examples demonstrated that the raw sinterhardening powder related to this invention makes it possible to obtainsinter hardened compacts with good mechanical properties and with lowmanufacturing costs. TABLE 1 Commonly used percentages and elements forthe examples 1-6 in the present invention and for cases A-D from theindustry and based on the Metal Powder Industries Federation(MPIF)standards (weight percentage, wt %) Element Ex: 1 Ex: 2 Ex: 3 Ex: 4 Ex:5 Ex: 6 Ex: A & B Ex: C Ex: D C 0.36%  0.34%  0.5% 0.5% 0.6% 0.4%0.4-0.6% <0.1% 0.6-0.9% Ni 8.0% 9.0% 4.0% 3.1% 4.0% 7.5% 1.5-2.5%6.5-8.5% 1.2-1.6% Mo 0.8% 0.8% 0.5% 0.5% 0.2% 0.8% 0.2-0.5% <0.5%1.1-1.4% Cr 0.8% 0.8% 3.0% 3.0% 1.5% 0.5% — — — Mn 0.6% — — — — — — —0.3-0.5% Cu — — — 1.0% — —. — — 1.0-3.0% Si 0.3% 0.3% — — — 0.3% <1.0<1.0 — Fe the rest the rest the rest the rest the rest the rest the restthe rest the rest

TABLE 2 Comparison of mechanical properties of the alloys among examples1-6 and examples A-D Quench- Density hardening Tensile strength Ex:(g/cm3) process (MPa) Hardness Ductility (%) 1 7.6 None** 1800 HRC45 3 27.6. None** 1780 HRC45 4 3 7.2 None** 1320 HRC39 2 4 7.1 None** 1280HRC38 2 5 7.3 None** 1270 HRC31 2 6 7.5 None** 1650 HRC43 4 A 7.5 None415 HRB62 15 B 7.5 Yes* 1655 HRC48 2 C 7.6 None 440 HRB69 26 D 7.2None** 1070 HRC40 <1*Austenizied at 860° C. and then oil quenched, then tempered at 180° C.for 2 hours.

**Sintered and then tempered at 180° C. for 2 hours.

In conclusion of the above description, compared to the best injectionmolding alloy, MIM-4605 (after quenching and tempering), and the bestsinter-hardening alloy, FLC2-4808, for the press-and-sinter work piece,listed by the Metal Powder Industries Federation (MPIF); thesinter-hardening composition of the present invention can attain similaror even better mechanical properties without the quench-hardeningprocess. Besides, the problems derived from quench-hardening in theprior art, including deformation, inconsistency of the dimensions, andcracking after quenching, etc, can be avoided in the present invention,and the costs from the quench-hardening process can be eliminated.Although sinter-hardening alloys have been available for the pressingprocess in traditional powder metallurgy, the cooling rate required forthe sintered compact is much higher than that required in this study.The sintered compact of the present invention provides excellentmechanical properties, and it also provides advantages in the areas ofdimensional control and lower costs.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A sinter hardening powder comprising iron (Fe) as its primarycomposition, 0.1 wt %-0.8 wt % of Carbon (C), 3.5 wt %-12.0 wt % Nickel(Ni), 0.1 wt %-7.0 wt % chromium (Cr), and 2.0 wt % or less ofmolybdenum (Mo), wherein a mean particle size of sinter hardeningpowders is 150 μm or less.
 2. The sinter hardening powder as recited inclaim 1, further comprising at least one element selected from the groupconsisting of 2 wt % or less Copper (Cu), 1 wt % or less Titanium (Ti),1 wt % or less Aluminum (Al), 1 wt % or less Manganese (Mn), 1 wt % orless Silicon (Si), 1 wt % or less Niobium (Nb), and 1 wt % or less ofPhosphorous (P).
 3. The sinter hardening powder as recited in claim 1,wherein the content of Carbon (C) is between 0.3 wt %-0.7 wt %, thecontent of Nickel (Ni) is between 6.0 wt %-10.0 wt %, the content ofchromium (Cr) is between 0.3 wt %-6.0 wt %, and the content ofmolybdenum (Mo) is between 0.1 wt %-1.0 wt %.
 4. The sinter hardeningpowder according to claim 2, wherein the content of Copper (Cu) isbetween 0.1 wt %-1.0 wt %, the content of Manganese (Mn) is between 0.1wt %-0.8 wt %, and the content of Silicon (Si) is between 0.1 wt %-0.5wt %.
 5. The sinter hardening powder as recited in claim 1, wherein asource of carbon is from graphite.
 6. The sinter hardening powder asrecited in claim 1, wherein a source of carbon is from carbonyl ironpowder.
 7. The sinter hardening powder as recited in claim 1, whereinthe mean particle size of the sinter hardening powders is between 0.1 μmand 30 μm, and the content of chromium (Cr) is between 0.1 wt % and 2 wt%.
 8. The sinter hardening powder as recited in claim 1, wherein themean particle size of the sinter hardening powders is between 30 μm and150 μm, the content of chromium (Cr) is between 1 wt % and 6 wt %. 9.The sinter hardening powder as recited in claim 1, wherein the sinterhardening powders are elemental powders, ferroalloy powders, or amixture thereof.
 10. The sinter hardening powder as recited in claim 9,wherein the ferroalloy powders and the elemental powders are diffusionalloyed or chemically bonded together.
 11. A granulated powder forsintering manufactured using the sinter hardening powder as recited inclaim 1, wherein a mean particle size of the granulated powder isbetween 20 μm-150 μm.
 12. The granulated powder for sintering as recitedin claim 11, wherein the mean particle size of the granulated powder isbetween 40 μm-80 μm.
 13. A sintered compact manufactured using thesinter hardening powder as recited in claim
 1. 14. A sintered compactmanufactured using the granulated powder as recited in claim 11.